This research proposal describes the design and development of a novel plasmid DNA vaccine formulation that will enhance DNA uptake by selected cell populations and improve the magnitude of the immune response using the expression of a co-stimulatory molecule. The proposed vaccine strategy involves the intramuscular (i.m.) injection of linear plasmid DNA encoding for HIV-2 antigens (gag/pol, tat, rev) as well as the B7-1 co-stimulatory molecule to direct the development of cytotoxic T-cells in the area of antigen expression. In addition, the DNA component of the vaccine is formulated with nanomeric calcium phosphate particles ranging from 300 to 350 nm in diameter prior to injection. These non-toxic biodegradable particles will bind a portion of the plasmid DNA and will be selectively taken up by tissue macrophages and invading antigen presenting cells, while remainder of the unbound plasmid DNA will be taken up and expressed by muscle cells in vivo. Both muscle cells and the tissue macrophages will express the HIV-2 antigens and the B7-1 co-stimulatory molecule to further enhance the cell mediated immune response against HIV-2 epitopes. Multiple domains of the same viral protein will be cloned and expressed by transfected cells in an attempt to address and overcome epitope dominance. This HIV-2 vaccine formulation will be evaluated for antigen and co-stimulatory molecule expression using cellular systems in vitro, prior to vaccination experiments in vivo using a primate model (M. nemistrina ). Vaccinated primates will be evaluated for the development of cytotoxic T-cells and antibody production against HIV-2 epitopes, with subsequent challenge with HIV-2 (287) to assess the immunoprotective capacity of this novel vaccine formulation.